Gaskets of said type can be of single-layer design. The subject matter of the present application is however a multi-layer gasket, as is known per se from the prior art.
A gasket of said type normally has a plurality of passage openings which extend through its layers, in particular one or more combustion gas openings, and further openings for fastening means, oil ducts, cooling water ducts and the like.
The gasket is composed of one or more sealing layers. In order to increase and ensure its sealing action, it is conventional to form a bead around the passage openings, in particular around the combustion gas openings, or else for example around the cooling water ducts, by means of corresponding deformation of at least one of the sealing layers, which bead generally completely encloses the passage opening or the passage openings.
In order to obtain the functionality of said beads, their excessive or complete plastic deformation as a result of compression during installation or during operation must be prevented. For this purpose, deformation limiters are conventionally used, which can also be referred to as stoppers. These are known in a wide variety of embodiments. They can for example be generated by bending the layers or one of the layers. It is however also conventional to form the one or more deformation delimiter(s) (stopper(s)) into the one or more sealing layer(s) in the form of embossings with a lower height than the bead height.
Finally, it is also already known to provide one of the layers of the multi-layer gasket as a spacer plate or stopper layer with the deformation limiter (stopper). The present invention relates to such a gasket type.
Here, the stopper can for example be arranged in the region between the bead and the combustion chamber, or else at the other side or at both sides of the bead.
Known are inter alia stoppers which extend as an annular band around a combustion chamber opening, which band is formed as a two-dimensional pattern of extruded cup-like depressions and elevations, with the elevations being formed by material of the sheet metal layer which is displaced during the embossing of the depressions, and each depression being situated directly opposite an elevation on the other side of the sheet metal layer, so that a diamond or chessboard pattern of elevations and depressions is generated on both sides of the sheet metal layer (EP 1577589 A1). Here, however, the elevations and depressions do not form a closed line.
In contrast, however, it has proven to be advantageous to design the stopper to be composed of a plurality of directly adjacent, directly adjoining ridge-shaped elevations and groove-shaped depressions which are formed in the spacer or stopper layer on its two sides, which elevations and depressions are assigned to the respective bead in order to limit its compression.
The successive elevations (ridges) and depressions (grooves) of the stopper can, in cross section, have the shape of a wave or of a toothing, in which the wave peaks and troughs or the tooth tips can also be flattened. It has also already been proposed to design the elevations and depressions to be rectangular in cross section, so as to generate rectangular webs (DE 196 41 491 A1) or profiled ribs (DE 2 145 482; JP 11-108191 A) and depressions which are correspondingly rectangular in cross section (so-called rectangular stoppers).
It has also already been proposed to form the elevations and depressions as ridges and grooves which are trapezoidal in cross section (DE 42 19 709 A1, DE 102 56 896 A1) or as waves which are trapezoidal in cross section (WO 01/96768 A1).
In each case, the amplitude of the elevations and depressions of the stopper is less than that of the beads which are to be protected.
WO 2006/005488 A1 criticizes the wave-shaped or sawtooth-shaped or also trapezoidal stoppers, which are mentioned above as being known, on account of their high elasticity and therefore reduced contact pressure. In the case of the rectangular stoppers, it is additionally objected to as being disadvantageous that their sharp-edged transitions between the elevations and depressions create the inherent risk of gasket parts breaking up.
In order to obtain the advantages of said known stoppers and at the same time to avoid their disadvantages, in particular to obtain their very rigid design and to nevertheless avoid damaging pressure peaks, it is proposed there to design the stopper such that, on the opposite sides of the spacer plate (of the stopper layer, referred to there as “other sealing layer”), depressions and elevations are alternately formed in such a way that a depression is situated at least partially opposite an elevation, that at least a part of the depressions and the elevations is substantially trapezoidal in cross section, with obliquely-running delimiting walls between the adjacently-arranged depressions and elevations of one side, and that the opposing delimiting walls, which are adjacent to one another, of two sides delimit a web cross section of the layer which is the same size as or greater than the cross section delimited between the opposing depressions of the two sides.
Although the teaching of making the cross section of the webs between adjacent, oblique delimiting walls of the trapezoidal elevations and depressions as thick as possible, specifically thicker than the cross section delimited between the depressions at both sides, leads to a considerable strengthening of the flanks of the trapezium and therefore to an increased stiffness of the stopper, and the trapezoidal design of the depressions simultaneously reduces the risk of breakage of parts of the stopper, albeit that this is the case only up to a certain degree, the stiffness which is gained is however not sufficient to give the stopper the fatigue strength which is actually required in use. This is attributed primarily to the fact that the stiffness of the stopper overall is adversely affected by the incisions of the depressions having to be relatively deep owing to the geometry of the stopper.
The geometric ratios of the cross sections in said stopper construction of the prior art also result in a very large amount of space being required for the stopper overall, both for the thickened portions and also for the embossings, in the case of which sufficient material must be displaced. Many gaskets do not offer the prerequisites necessary for this.
Proceeding from said prior art, it is the object of the invention to provide a multi-layer metallic flat gasket with a stopper which has the required high fatigue strength (stiffness and breaking resistance), and at the same time can be produced more simply and cost-effectively.